an array of arrays varied in length in R - arrays

Question

I use R for my statistical analysis.
I wanna group my data in an array based on the ID column. This results in having an array of unique IDs which each cell includes a data array of correspondence ID. Since the number of the data per ID is not similar, therefor each array in each cell has different length.
So I wonder how I can create an array of arrays varied in length using R?
I already having the following codes but get an error:
#number of unique IDs
size<-unique(data[,1]);
for (i in 1:length (gr))
{
index<- which(data[,1]==gr[i]);
data_c[[i,1]]<-data[index,];
}
Here is the error
more elements supplied than there are to replace
Thanks in advance for any comment.
I explain my problem by an example:
I have following data called it DATA_ALL:
DATA_ALL[]=
id age T1 T2 T3 T4
1 20 1 0 0 0
1 20 NA 0 NA 0
1 20 0 0 0 0
5 30 1 NA 0 0
5 30 0 0 0 1
6 40 0 1 0 0
I want to group the data of each id and put all in an array (array of arrays):
DATA_GROUPED []=
id data
1 1 X1[]=[an array includes all data from DATA_ALL where the id=1]
2 5 X2[]=[an array includes all data from DATA_ALL where the id=5]
3 6 X3[]=[an array includes all data from DATA_ALL where the id=6]
Please note that the length of X1!=X2!=X3
So how I can create the DATA_GROUPED[] matrix??

Answer 1

It is nearly impossible to answer your question in relation to your code, but in general, I think what you want to do is create a list of vectors, a bit like this:
one<-letters[1]
two<-letters[2:3]
three<-letters[4:6]
combined<-list(one=one, two=two, three=three)
Be sure to use indexing correctly now, and preferably with [[:
for(i in 1:length(combined))
{
cat("The contents of item", names(combined)[i], "are:", combined[[i]], "\n")
}
Output:
The contents of item one are: a
The contents of item two are: b c
The contents of item three are: d e f
Edit (following edit of question):
split.data.frame(DATA_ALL, DATA_ALL[,1])
Check ?split and note the first paragraph in Details.
Note this indeed creates a list of matrices/arrays.